If you're looking for a perennial with all-summer display, consider globe thistle (Echinops ritro).
Its 1- to 2-inch, globe-shaped flower heads start out steely blue in early summer and turn bright blue as the summer progresses. It has unique, thistle-like dark green leaves with deep lobes, wavy margins, and a downy white underside. Plant this low-maintenance perennial in the back of the border near other perennials that enjoy similar growing conditions. Coneflowers, garden phlox, and ornamental grasses are good partners.
Common name: Globe thistle
Botanical name: Echinops ritro
Plant type: Clump-forming perennial
Height: 24 to 36 inches
Zones: 3 to 9
Sun: Full sun
Soil: Poor to average well-drained soil
Moisture: Moderate to dry
• Mulch: Mulch with 2 inches of organic compost to deter weeds.
• Fertilizer: Add a light application of organic fertilizer when planting.
• Pruning: Deadhead spent flowers if you want to prevent self-seeding. In warmer climates, deadheading will encourage a second bloom.
• ‘Veitch's Blue' (pictured) has flower heads that are more blue than the species and is a good choice for fresh-flower arrangements. Blooms reach 3 to 4 feet tall. Zones 3 to 9.
• ‘Taplow Blue' has gray-blue flowers. Grows 2 to 4 feet tall. Zones 3 to 9.
• Does best in poor, sandy soils. May require staking in rich soils.
• Pastel pink flowers complement foliage and blue flowers.
• Forms beautiful, spiny, globe-shaped dried flower heads on sturdy stems. To dry flower heads, cut and place in a warm, dry spot.
• Use caution because plant can be rough on unprotected hands and feet.
Pests and diseases
• Not susceptible to insects and disease.
• Divide from fall to late spring, but keep in mind that its large taproot makes division difficult.
• Sow seeds in spring.
All in the family
• Echinops giganteus has gray-blue flower heads. Foliage is similar to Echinops ritro, but it grows 15 feet tall. Zones 4 to 8.
• Echinops bannaticus has gray-blue flowers and grows 1½ to 4 feet tall. Zones 5 to 9.
• The Asteraceae family is a huge family that includes yarrow, golden marguerite, aster, cornflower, and gazania.
Photo courtesy of Missouri Botanical Garden PlantFinder